1. Field of the Invention
The present invention relates generally to a method and apparatus for fabricating semiconductor devices and, in particular, to a method and apparatus for cleaning a substrate surface by, for example, eliminating polysilicon defects induced by metallic contaminants.
2. Description of Related Art
In the production of semiconductor devices, a semiconductor substrate, such as a silicon substrate, may be formed comprising a number of varying block levels or layers whereby such block levels may include various structures formed over the semiconductor substrate. For example, block levels may include varying structures over the silicon substrate which define the semiconductor devices such as resistors, PFET wells and NFET wells in CMOS technology, and the like.
As will be recognized, the varying structures, or varying block levels, may be made by processes including photolithography, ion implant, resist strip, wet cleaning processes, and the like. An inherent problem of these block levels, and the processes used to define them over the silicon substrate, is that they produce contaminants including, for example, metallic contaminants and hydrocarbon-containing contaminants over the substrate which remain thereon to contaminate the surface. During the semiconductor manufacturing process, contaminants including metallic contaminants and hydrocarbon-containing contaminants may be deposited on both the substrate front-side (chip side) and back-side. Front-side contaminants are typically introduced from trace metallics in the photoresist while backside contaminants are typically introduced from the semiconductor processing equipment such as, for example, automated substrate handlers and chucks. This invention addresses both substrate front-side and back-side metallic removal.
As will be further recognized, if the metallic contaminants are not removed from the substrate front-side or back-side prior to either the gate oxidation or the polysilicon deposition processes, a gross defect may be induced. It is preferable to remove the contaminants prior to gate oxidation to reduce the potential for gate oxide “pinholes”. These “pinholes” can render the device either non-functional or unreliable due to poor gate oxide integrity. Additionally, removal of the metallic contaminants will prevent the formation of polysilicon defects, herein referred to as “peppery polysilicon”, which can result in shorts between polysilicon lines.
The microelectronics industry has faced problems with peppery polysilicon since it first started using polysilicon as a gate conductor. Several techniques are aimed at controlling peppery polysilicon including, for example, reducing the metallics within the deposited photoresist, and improving both the dry steps and wet clean steps used to define the various block levels. However, such prior art techniques do not completely eliminate the metallic contaminants over the substrate surface, and thus do not prevent the occurrence of peppery polysilicon. Therefore, known techniques can still lead to semiconductor failure in the field.
Prior art is also directed to controlling contaminants within the deposition tools used for gate formation. For instance, in U.S. Pat. No. 3,279,946, a process is disclosed wherein a reactor chamber, or a conventional semiconductor deposition tool, is preconditioned prior to a semiconductor material deposition. The tool is preconditioned by heating the reactor in the presence of a reactant gas, preferably HCI or chlorine, which reacts with donor impurities on the walls of the chamber to merely remove impurities in the reactor prior to a semiconductor material deposition on a clean wafer. This approach is problematic as the chlorine eventually induces corrosion of the deposition tooling in the reactor whereby the corrosion can actually increase metallic contamination during the semiconductor material deposition. Since the prior art does not describe any in-situ cleaning of metal contaminants from a substrate surface, or cleaning of the corroded deposition tooling, peppery polysilicon will likely result and the semiconductor may fail.
Furthermore, as semiconductor technologies, such as CMOS technologies, continue to decrease in size, and thus require thinner transfer gate oxides, the known cleaning and/or metallic contamination removal processes do not completely clean the substrate surface and/or eliminate metallic contaminants from the substrate surface. For example, the process of removing metallic contaminants from a substrate surface using a chlorinated environment during gate oxidation transfer processes is used for thick gate oxide depositions. In such processes, the metallics are removed as a result of the substrate being exposed to the chlorinated environment for the extended period of time it takes to deposit the thick gate oxide. However, such techniques are not effective or efficient in removing metallic contaminants from substrates having thin gate oxide. To produce the thinner gate oxide the substrate will be exposed to the chlorinated environment for a limited time since the gate oxide deposition time is reduced to produce the thinner gate oxide. Thus, metallic contaminants may remain on the thin gate oxide resulting in peppery polysicon, as well as pinholes in the thinner gate oxide, whereby gate oxide integrity may be compromised, and polysilicon shorts and semiconductor failure may occur.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method and apparatus which cleans and/or removes contaminants, including metallic contaminants and hydrocarbon-containing contaminants, from a surface of a substrate to provide the substrate with a clean surface for uniform gate formation.
It is another object of the present invention to provide a method and apparatus to clean and/or reduce residual metallic contamination on a surface of a semiconductor substrate after completion of all block levels.
A further object of the present invention is to provide a method and apparatus to clean and/or reduce residual metallic contamination on a surface of a semiconductor substrate prior to sacrificial oxide removal.
Another object of the present invention is to provide a method and apparatus of preventing oxides formed on a semiconductor substrate surface prior to gate formation.
Still another object of the present invention is to provide a method and apparatus of forming a clean surface on a semiconductor substrate to provide for a high quality gate oxide transfer.
It is also an object of the present invention to provide a method and apparatus for the uniform formation of a gate oxide layer across the surface of a semiconductor substrate.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.